A Billion, Million and Thousand of People

Nothing is special with 100,000 people lives in the same places (city). People in the past can achieve that. They can built the pyramid. Even to build a city of 1,000,000 population is not difficult -Rome can achieved that.

100,000 people lives in city. In ancient civilization such as Memphis Egypt 100K, India & China 400K 200 BC, Babylon 200K 400 BC, Greek 8 BC 700K. City is only 10% size of the empire or civilization. Greek is around 5 million, Egypt 7 million. In ancient Egypt, Pyramids can be built with 20,000 people.

1,000,000 people, Western Civilization: Alexandria 1000 BC, Rome 2 AD, Baghdad 1000 AD. Rome is special caxe because its empire is the biggest having 56 million population. Post Industrilization game is different. 1,000,000 people working together called Industrial Revolution in 1800.

10,000 population of Batavia achieved in 1700, London in Rome is around 50,000, New York at its settlement is 7,000

World Population Growth:

200,000 years ago, 2 homo sapiens appear in africa

100,000 years ago, 100,000 people lives on earth

70,000 years ago, 1,000 people lives on earth (declined due to Toba)

10,000 years ago, 2,000,000 people lives on earth

2000 years ago, 200,000,000 people lives on earth

200 years ago, 1,000,000,000 people lives on earth

Increase in brain size for early H. sapiens has significant metabolic consequences, because the human brain, which is 2% of the body weight, uses some 20%–25% of its metabolic energy. Body size increase from the australopithecines would require a 40%–45% increase in the total energy expenditure of early H. sapiens. The payoff for early H. sapiens populations, and the source of the additional energy, was in the higher-quality diet with its concentrated energy sources and the predictable use of more resources provided by the newly developed hunting, gathering, and scavenging strategy.Population Bottlenecks and Pleistocene Human Evolution (Molecular Biology and Evolution, 1999)

1000 years ago, Merapi Erupted. It buried largest budhist temple, it might also burried largest kingdom in Java at that time.

Wiki
Classical Demograpy
Demography of the Roman Empire
List of largest cities throughout history